If you want to be really paranoid, go by the breaker on the circuit. Otherwise, assuming you don't want to actually pull up the unit to check it's plate rating, if you have an ampmeter you can get an estimate. The better ones should have some sort of max or peak rating - this will tell you what it needs when starting up, then when it settles down a regular reading will work.
If you don't have the max capability - 2-3X average for startup.
Then add all the stuff up, and realize you can't start everything at the same time.
There are a pair of fuses (one for each phase). I can't remember the rating, and now I can't find the spares that I thought we had :( There is also a breaker out on the pole IIRC.
I wouldn't be trying to run everything at any rate. Just pump up some water to use, and maybe run the freezer for a little while each day if the "tribulation" comes in summer.
